So, it sounds like Serris and StarFall are in favor of Zyanya and Nixx being sleeper agents, Nick is not.
Nick, it wouldn't be quite the same as StarFall's plot twist, because Starfall's characters were willingly and knowingly preparing to betray the group. Nixx and Zyanya honestly believed they were valid teammates until the moment Trinity (for example) flicks the switch and suddenly their minds are taken over and they're assaulting the team. They would be
Manchurian Agents as opposed to
Moles, like Starfall's team.
In addition, I won't kill Zyanya, since it sounds like you want her to hook up with Landon. And right now, there isn't much more for Shelton's team to do. Once they reach the cargo bay and open it, the oil rig sinks, so they can't do that until the other plot threads are tied up.
James' team has to fight Death, James himself has to fight O'Neil, Kerzach has to fight Zenarchis. Aimee has to fight Trinity but I plan to have her do it alone. It'll provide a bit of distraction and let Shelton's bodyguards show off some ingenuity. Plus if Aisha is involved in stopping Nixx it'll provide some character interaction between the two.